#include <iostream>
#include <string>

int main() {
    char input;
    std::cout << "please input " << std::endl;
    std::cin >> input;
    if (input <= 95 && input >= 65) {
        input = input + 32;
        std::cout << input << std::endl;
    } else if (input <= 121 && input >= 97) {
        input = input - 32;
        std::cout << input << std::endl;
    } else {
        std::cout << "invalid input" << std::endl;
    }

    return 0;
}